Spotting and low heartbeat.

So.... we thought we were about 8 weeks pregnant - but went for our first ultrasound yesterday and doc said the heartbeat is weak and lower than he would like if the weeks are correct ... I have been spotting since Thursday... no morning sickness, no vomiting, no pregnancy symptoms or than extreme fatigue. Anyone else experience anything like this —- what are your thoughts? Worried and stressed which doesn’t help